Flowmeter

ABSTRACT

An outlet port in the upper end of a fluid flow passageway vertically formed in a flow rate measuring section ( 8 ) disposed in a fluid storage recess ( 23 ) communicating with a fluid inlet pipe through an opening ( 21   a ) communicates with a fluid outlet pipe ( 22 ) through an opening ( 22   a ). The heat type flow rate sensor ( 10 ) disposed in the flow rate measuring section ( 8 ) has a fin plate projecting into the fluid flow passageway through a sensor mount hole ( 8   c ). The flow rate measuring section ( 8 ) is formed with an auxiliary flow passageway for leading the fluid within the fluid storage recess ( 23 ) to the inlet port ( 811 ) in the lower end of the fluid flow passageway, the auxiliary flow passageway extending in parallel with the fluid flow passageway and having fluid introducing ports ( 822, 823, 824 ) and a fluid delivering port ( 821 ) leading to the fluid flow passageway. The flow rate measuring section ( 8 ) is equipped with a bottom plate ( 8   d ) forming a communication passageway extending from the fluid delivering port ( 821 ) to the fluid flow passageway inlet port ( 811 ).

This application is a 371 of PCT/JP01/11372 filed on Dec. 25, 2001,published on Jul. 11, 2002 under publication number WO 02/054021 A1 andclaims priority benefits of Japanese Patent Application No. 2000-398478filed Dec. 27, 2000.

TECHNICAL FIELD

The present invention relates to a fluid flow rate sensing technique,particularly to a flowmeter for measuring a momentary flow rate orintegrated flow rate of a fluid which flows in a pipe.

BACKGROUND ART

A flowmeter has been used in sensing flow rates of fluids such askerosene, water, and gas consumed by households or companies. As theflowmeter, a flowmeter using a heat type (especially an indirectlyheated type) flow rate sensor, whose cost can easily be reduced, hasbeen used.

For the indirectly heated type flow rate sensor, a sensor has been usedincluding a sensor chip constituted by using a thin-film technique on asubstrate to stack a thin-film heating material onto a thin-filmtemperature sensing material via an insulating layer so that heat can beconducted between the sensor chip and fluid in a pipe (including a fluidflow passageway connected to an external pipe and disposed in theflowmeter). When the heating material is energized, the temperaturesensing material is heated to change electric characteristics of thetemperature sensing material such as a value of electric resistance.This change of the electric resistance value (based on a temperaturerise of the temperature sensing material) responds to a flow rate (flowvelocity) of the fluid which flows in the pipe. This is because a partof a heating value of the heating material is transmitted into thefluid, an amount of heat diffused into the fluid changes in accordancewith the flow rate (flow velocity) of the fluid, the amount of heatsupplied to the temperature sensing material accordingly changes, andthe electric resistance value of the temperature sensing materialchanges. The change of the electric resistance value of the temperaturesensing material also differs with temperature of the fluid. Therefore,another method comprises: incorporating a temperature sensing elementfor compensating for the temperature into an electric circuit formeasuring the change of the electric resistance value of the temperaturesensing material so as to minimize the change of a measured flow ratevalue by the temperature of the fluid.

This indirectly heated type flow rate sensor using a thin-film elementis described, for example, in JP(A)-11-118566. In this flow rate sensor,the electric circuit including a bridge circuit is used to obtain anelectric output corresponding to the flow rate of the fluid.

In the above-described flowmeter, a fin plate for heat exchange betweenthe sensor chip and the fluid is projected into the fluid flowpassageway. In the vicinity of the flow rate sensor, an electric circuitportion including a circuit substrate for flow rate calculation, adisplay portion, a communication circuit connection portion, and thelike are disposed. A function portion of the flowmeter including theseportions is entirely contained in a housing.

In the related-art flowmeter, a path for fluid circulation in thehousing is not simply linear, and is formed in a bent shape in manycases. This is because a filter for removing foreign particles in thefluid is disposed in the circulation path, or the circulation path isformed so as to alleviate an influence of rapid temperature change ofthe inflowing fluid and to relatively moderate the temperature change ofthe flow rate sensor. On the other hand, the temperature in the housingis easily influenced by outside air temperature or direct sunlight.Therefore, there are problems that nonuniformity of temperaturedistribution by a position in the housing including the circulated fluidbecomes remarkable and that accuracy of flow rate sensing easily drops.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to provide a heat typeflowmeter in which there is little nonuniformity by a position oftemperature distribution inside a housing including a circulated fluidand in which there is little accuracy drop of flow rate sensing.

To achieve the above-described object, according to the presentinvention, there is provided a flowmeter comprising:

-   -   a fluid storage portion formed in a housing, the fluid storage        portion being connected to a fluid inlet tube formed in the        housing; and    -   a flow rate measuring portion which is disposed in the fluid        storage portion and in which a fluid flow passageway is formed        and an outlet port of the fluid flow passageway is connected to        a fluid outlet tube formed in the housing and in which a heat        type flow rate sensor is disposed including a fin plate        projecting into the fluid flow passageway,    -   wherein an auxiliary flow passageway for leading fluid in the        fluid storage portion toward an inlet port of the fluid flow        passageway is formed in the flow rate measuring portion, and the        auxiliary flow passageway comprises a plurality of fluid        introducing ports and a fluid discharging port which is        connected to the fluid introducing ports and which is positioned        closer to the fluid flow passageway inlet port than to the fluid        introducing ports.

In one aspect of the present invention, one of the plurality of fluidintroducing ports of the auxiliary flow passageway is constituted of oneend opening, the other fluid introducing ports are constituted of sideopenings, and the fluid discharging port is constituted of the other endopening. In one aspect of the present invention, the fluid flowpassageway extends in a vertical direction, the auxiliary flowpassageway extends in parallel with the fluid flow passageway, and thefluid flow passageway inlet port is positioned in a lower end of thefluid flow passageway.

In one aspect of the present invention, the fluid storage portion isformed of a recess portion for storage formed in a main body member ofthe housing and an inner lid member fitted to the recess portion, andthe flow rate measuring portion is attached to the inner lid member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing a whole constitution of aflowmeter according to the present invention;

FIG. 2 is a sectional view of a flow rate measuring portion;

FIG. 3 is a side view of the flow rate measuring portion;

FIG. 4 is a diagram showing an attaching portion of a flow rate sensor;

FIG. 5 is a sectional view of the flow rate sensor;

FIG. 6 is an exploded perspective view showing fluid circulation in theflowmeter according to the present invention;

FIG. 7 is a block diagram showing a schematic constitution of anelectric circuit portion of the flowmeter according to the presentinvention;

FIG. 8A is a diagram showing measurement ranges of a flow velocitydistribution and temperature distribution in a fluid storage portion ofthe flowmeter according to the present invention;

FIG. 8B is a diagram showing the measurement ranges of the flow velocitydistribution and temperature distribution in the fluid storage portionof a related-art flowmeter;

FIG. 9 is a graph showing the flow velocity distribution in the fluidstorage portion;

FIG. 10 is a graph showing the flow velocity distribution in the fluidstorage portion;

FIG. 11 is a graph showing the temperature distribution in the fluidstorage portion; and

FIG. 12 is a graph showing the temperature distribution in the fluidstorage portion.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described hereinafterwith reference to the drawings.

FIG. 1 is a schematic exploded perspective view showing a part of aconstitution of one embodiment of a flowmeter according to the presentinvention. A housing main body member 2 of the flowmeter is die-cast inaluminum or zinc. To the housing main body member 2, an outer lid member(not shown) of die-cast in aluminum or zinc is fitted by screwengagement in a specific direction (direction of arrow A). A fluidoutlet tube 22 is formed on one side of a rear surface upper portion ofthe housing main body member 2, and a fluid inlet tube (not shown) isformed on the other side.

A recess portion 23 for fluid storage portion is formed in an upper halfof the housing main body member 2. An outer peripheral surface of adie-cast inner lid member 6 of aluminum or zinc is fitted by screwengagement to an end surface of an inner wall 26 of the recess portion23 in a direction of arrow A so as to seal the recess portion 23. In thefitting, a rubber seal (cork-mixed rubber seal, and the like) isdisposed to prevent the fluid from leaking from the fitted portion.Thus, a fluid storage portion is formed between the housing main bodymember 2 and the inner lid member 6 to temporarily store and circulatethe fluid. In the housing main body member 2, an opening is connected tothe fluid inlet tube and opened in the recess portion 23, and aconnection opening 22 a is connected to the fluid outlet tube 22 andopened in the recess portion 23.

A flow rate measuring portion 8 disposed in the fluid storage portion isattached to the inner lid member 6. FIG. 2 shows a sectional view of theflow rate measuring portion 8, and FIG. 3 shows a side view of theportion. In the flow rate measuring portion 8, a fluid flow passageway81 is formed to extend in a vertical direction (perpendiculardirection). An inlet port 811 of the fluid flow passageway 81 ispositioned in a lower part of the flow rate measuring portion 8. Aprotrusion 8 a projecting in the direction of arrow A is attached to anoutlet port 812 positioned in an upper part of the fluid flow passageway81. The inner lid member 6 is fitted to the housing main body member 2to thereby connect the protrusion 8 a to the connection opening 22 a ona housing main body member 2 side via a joint member 27. Thus, the fluidflow passageway outlet port 812 of the flow rate measuring portion 8 isconnected to the fluid outlet tube 22.

In sensor mount holes 8 b, 8 c formed in the flow rate measuring portion8 in the direction of arrow A, heat type flow rate sensors (to which afluid temperature detecting sensor is attached) 10 are insertedincluding fin plates which are heat conductive members for heatexchange, respectively (FIG. 1 shows only one heat type flow ratesensor). FIG. 4 shows an attaching portion of the flow rate sensor 10,and FIG. 5 shows a sectional view of the flow rate sensor 10. The flowrate sensor 10 inserted in the sensor mount hole 8 b via an O-ring isprojected into the fluid flow passageway 81. The flow rate sensor 10inserted in the sensor mount hole 8 c via an O-ring is projected into afluid storage space.

The flow rate sensor 10 includes a flow rate sensor portion 101 andfluid temperature detecting sensor portion 102. In the flow rate sensorportion 101, as shown in FIG. 5, a fin plate FP is bonded to a flow ratesensing portion FS by a bond material AD satisfactory in heatconductivity, and electrode pads of the flow rate sensing portions FSare connected to external electrode terminals ET by bonding wires BW.The fluid temperature detecting sensor portion 102 can be structured touse a fluid temperature sensing portion instead of the flow rate sensingportion FS in the flow rate sensor portion 101, and includes thecorresponding external electrode terminals ET. For these flow ratesensing portion and fluid temperature sensing portion, those describedin the above-mentioned JP(A)-11-118566 can be used. The flow rate sensorportion 101 and fluid temperature detecting sensor portion 102 aresealed and united with a common mold resin MR.

As shown in FIG. 2, a wire mesh cover MM for covering the fin plate FPof the flow rate sensor 10 inserted in the sensor mount hole 8 c isattached to the flow rate measuring portion 8. The wire mesh cover MM isdisposed in such a manner that the fin plate FP of the flow rate sensor10 may be influenced by fluid circulation based on natural convectionbut is prevented from being influenced by the fluid circulation causedby fluid supply. This flow rate sensor constitutes a reference flow ratesensing circuit which senses a difference of thermal properties of afluid to be measured with respect to a reference fluid for use inpreparing a calibration curve for use in converting an output valueobtained from a measured flow rate sensing circuit including the flowrate sensor 10 inserted in the sensor mount hole 8 b to a flow ratevalue.

As shown in FIG. 1, a fluid circulation path defining member 9 isdisposed in the recess portion 23. The fluid circulation path definingmember 9 defines a circulation path of the fluid flowing via the openingin the fluid storage portion, and uniformly guides the fluid into aregion in which the flow rate measuring portion 8 is disposed through avertically elongated opening formed between the defining member and theinner lid member 6.

Although not shown, an analog circuit substrate electrically connectedto the external electrode terminals ET of the flow rate sensor 10 isattached to a front surface of the inner lid member 6. Although notshown, circuit members such as a digital circuit substrate constitutingthe flow rate sensing circuit together with the analog circuitsubstrate, a transformer constituting a power supply circuit portion,and input/output terminal portions with respect to the flowmeter areattached to the outer lid member. Especially, the transformer andinput/output terminal portions are disposed in a recess portion 24 forthe circuit members formed in a lower half of the housing main bodymember 2.

As shown in FIGS. 1 to 3, the fluid flow passageway 81 of the flow ratemeasuring portion 8 extends in the vertical direction (perpendiculardirection). In the flow rate measuring portion 8, an auxiliary flowpassageway 82 is formed in parallel with the fluid flow passageway 81.The auxiliary flow passageway 82 includes a lower end opening which is afluid discharging port 821, an upper end opening which is a first fluidintroducing port 822, and two side openings positioned in heightsdifferent from each other which are second and third fluid introducingports 823, 824.

The auxiliary flow passageway 82 has a function of: introducing thefluid in the fluid storage portion via the fluid introducing ports 822,823, 824 and discharging the fluid via the fluid discharging port 821;and guiding the fluid toward the fluid flow passageway inlet port 811via a communication path constituted with use of a bottom plate 8 d. Thefluid introducing ports 822, 823, 824 have inner diameters which aredifferent from one another, and the inner diameter of the port having asmaller distance from the fluid discharging port 821 is set to besmaller. Accordingly, the flow rates of the fluids introduced into theauxiliary flow passageway 82 from the different heights can be averaged.

FIG. 6 is an exploded perspective view showing the fluid circulation inthe present embodiment. In FIG. 6, circulation directions of the fluidare shown by arrows. The fluid supplied from a fluid supply source (notshown) through piping is supplied into the fluid storage portion fromthe fluid inlet tube through an opening 21 a. The supplied fluid firstflows over the circulation path defining member 9 and reaches the regionwhere the flow rate measuring portion 8 is disposed. Subsequently, thefluid is sucked into the fluid flow passageway 81 via the auxiliary flowpassageway 82, discharged from the fluid outlet tube 22 through thefluid flow passageway outlet port 812 and the connection opening 22 a,and supplied into a fluid requiring apparatus (not shown). Thereafter,when there is a demand for the fluid on a fluid requiring apparatusside, the fluid is supplied into the fluid requiring apparatus from thefluid supply source via the auxiliary flow passageway 82 and fluid flowpassageway 81 in the fluid storage portion of the flowmeter.

In the present embodiment, the auxiliary flow passageway 82 is disposedin a position having a distance from the opening 21 a, which is largerthan that of the connection opening 22 a, and the auxiliary flowpassageway 82 is disposed adjacent to the inner wall 26 on the rightside in the fluid storage portion. Therefore, the flow toward the rightinner wall 26 in a horizontal direction, which is averaged concerning avertical position, is generated in the fluid in the fluid storageportion. Therefore, the temperature distribution in the fluid storageportion including the flow rate measuring portion 8 is sufficientlyuniformed, and accuracy of flow rate measurement is enhanced.

The fluid flow rate in the fluid flow passageway 81 is measured usingthe measured flow rate sensing circuit including the flow rate sensorportion 101 and fluid temperature detecting sensor portion 102 as shownin FIG. 7. In FIG. 7, in the flow rate sensor portion 101, a flow ratesensing portion is formed by stacking a heater onto a temperaturesensing resistor Tw via an insulating film, and a part of heating valueof the heater is conducted to the fluid circulated in the fluid flowpassageway 81 via the fin plates FP. The temperature sensing resistor Twexecutes temperature sensing while influenced by thermal interactionwith the fluid. Two resistors including the temperature sensing resistorTw and a temperature sensing resistor To of the fluid temperaturesensing portion of the fluid temperature detecting sensor portion 102form a bridge circuit. An output of the bridge circuit is amplified byan amplifier circuit, and compared with a predetermined value by acomparator, and an output of the comparator is inputted into a heatercontroller. The heater controller controls the heating of the heater ofthe flow rate sensor portion 101 via a buffer in response to an inputsignal. This control is performed in such a manner that the temperaturesensing resistor Tw of the flow rate sensor portion 101 maintains apredetermined temperature sensing state, that is, an input signal intothe heater controller maintains a predetermined value. This controlstate corresponds to a momentary flow rate, and the data is inputtedinto a flow rate conversion circuit.

The reference flow rate sensing circuit includes a constitution equal tothat of the measured flow rate sensing circuit except that a flow ratesensor portion 111 and fluid temperature detecting sensor portion 112similar to the flow rate sensor portion 101 and fluid temperaturedetecting sensor portion 102 are included, and performs similar flowrate sensing. Since the reference flow rate obtained thereby changes inaccordance with dynamic viscosity of the fluid to be measured, the flowrate measured by the measured flow rate sensing circuit can be correctedbased on an output of the reference flow rate sensing circuit.

A signal indicating the temperature of the analog circuit portion isinputted into the flow rate conversion circuit from a temperature sensorcircuit 12 including a temperature sensor (not shown). The flow rateconversion circuit performs operations such as correction in accordancewith the analog circuit portion temperature and correction in accordancewith the reference flow rate based on measured flow rate data obtainedfrom the measured flow rate sensing circuit, reference flow rate dataobtained from the reference flow rate sensing circuit, and analogcircuit portion temperature data obtained from the temperature sensorcircuit 12. The circuit also performs conversion into a flow rate valueusing a calibration curve.

A CPU including the above-described heater controller and flow rateconversion circuit is connected to a display portion, communicationcircuit, EEPROM, and reference clock. The obtained flow rate value isdisplayed in the display portion, or outputted to the communicationcircuit for use in communication with the outside.

Next, examples of a flow velocity distribution and temperaturedistribution in the fluid storage portion at a flow rate of 10 liters/hin the flowmeter of the present invention will be described withreference to FIGS. 8A and 9 to 12. For comparison, with reference toFIGS. 8B and 9 to 12, the flow velocity distribution and temperaturedistribution in the fluid storage portion at the flow rate of 10liters/h in a related-art flowmeter will be described.

FIGS. 8A and 8B show measurement ranges in the fluid storage portion.FIG. 8A shows the portion according to the present invention, and FIG.8B shows the portion according to the related art. The portion accordingto the present invention was one described in the embodiment withreference to FIGS. 1 to 7. For the related-art portion, the auxiliaryflow passageway 82 according to the present invention was removed, thebottom plate 8 d is excluded, and the fluid flow passageway inlet port811 directly opens into the fluid storage portion. A depth of the recessportion 23 for the fluid storage portion, that is, a width of the fluidstorage portion (Z-direction dimension in FIGS. 8A and 8B) was 18 mm,and measurement ranges [1] to [3] were in positions at 9 mm from thebottom of the recess portion 23 in a Z direction.

FIG. 9 shows the flow velocity distribution in the measurement ranges[1] and [2], and FIG. 10 shows the flow velocity distribution in themeasurement range [3]. In the present invention, dispersion of the flowvelocity is less than that of the related art in a broad range in eachmeasurement range. It is also seen that uniformity of the flow velocityover all the measurement ranges is higher than that of the related art.

FIG. 11 shows the temperature distribution in the measurement ranges [1]and [2], and FIG. 12 shows the temperature distribution in themeasurement range [3].

In the present invention, the dispersion of the temperature is less thanthat of the related art in the broad range in each measurement range. Itis also seen that the uniformity of the temperature over all themeasurement ranges is higher than that of the related art.

INDUSTRIAL APPLICABILITY

As described above, according to a flowmeter of the present invention,since an auxiliary flow passageway is disposed, an averaged flow of afluid is generated in a fluid storage portion and, thereby temperaturedistribution in the fluid storage portion including a flow ratemeasuring portion is sufficiently uniformed and accuracy of flow ratemeasurement is enhanced.

1. A flowmeter comprising: a fluid storage portion formed in a housing,the fluid storage portion being connected to a fluid inlet tube formedin the housing; and a flow rate measuring portion which is disposed inthe fluid storage portion and in which a fluid flow passageway is formedand an outlet port of the fluid flow passageway is connected to a fluidoutlet tube formed in the housing and in which a heat type flow ratesensor is disposed including a fin plate projecting into the fluid flowpassageway, wherein an auxiliary flow passageway for leading fluid inthe fluid storage portion toward an inlet port of the fluid flowpassageway is formed in the flow rate measuring portion, and theauxiliary flow passageway comprises a plurality of fluid introducingports and a fluid discharging port which is connected to the fluidintroducing ports and which is positioned closer to the fluid flowpassageway inlet port than to the fluid introducing ports.
 2. Theflowmeter according to claim 1, wherein one of the plurality of fluidintroducing ports of the auxiliary flow passageway is constituted of oneend opening, the other fluid introducing ports are constituted of sideopenings, and the fluid discharging port is constituted of the other endopening.
 3. The flowmeter according to claim 2, wherein the fluid flowpassageway extends in a vertical direction, the auxiliary flowpassageway extends in parallel with the fluid flow passageway, and thefluid flow passageway inlet port is positioned in a lower end of thefluid flow passageway.
 4. The flowmeter according to claim 1, whereinthe fluid storage portion is formed of a recess portion for storageformed in a main body member of the housing and an inner lid memberfitted to the recess portion, and the flow rate measuring portion isattached to the inner lid member.
 5. The flowmeter according to claim 2,wherein the fluid storage portion is formed of a recess portion forstorage formed in a main body member of the housing and an inner lidmember fitted to the recess portion, and the flow rate measuring portionis attached to the inner lid member.
 6. The flowmeter according to claim3, wherein the fluid storage portion is formed of a recess portion forstorage formed in a main body member of the housing and an inner lidmember fitted to the recess portion, and the flow rate measuring portionis attached to the inner lid member.